Liquid crystal projectors including liquid crystal display units are disclosed, for example, in Unexamined Japanese Patent Publications SHO 61-150487 and SHO 64-74585.
FIG. 11 shows an example of such liquid crystal projectors. The illustrated projector has a projection lens 13 mounted on the front wall of a case 11, and a light source 12 opposed to the lens 13 and disposed at the rear end of the case 11 inside thereof.
A liquid crystal display unit 8 of the active matrix type is disposed between the light source 12 and the projection lens 13 on the optical axis. Blue light dichroic mirrors 14, 14a and red light dichroic mirrors 15, 15a are arranged, each as inclined at 45 degrees with the optical axis, between the liquid crystal unit 8 and the light source 12, and between the unit 8 and the projection lens 13.
Reflectors 16, 16a and 17, 17a are arranged as opposed to the respective dichroic mirrors 14, 14a and 15, 15a in parallel thereto, with liquid crystal units 8b and 8a interposed between the reflectors 16, 16a and between the reflectors 17, 17a, respectively.
Of the light emitted by the light source 12, the green light component passes through the dichroic mirrors 14, 15 and impinges on the liquid crystal unit 8, and the red light component and blue light component are respectively separated off by the red light dichroic mirror 14 and the blue light dichroic mirror 15 which are closer to the light source 12, are then reflected at the reflectors 16, 17 closer to the light source 12 and impinge on the respective liquid crystal display units 8b, 8a. When passing through the liquid crystal display unit, each light component is modulated with image data. The light components are combined again by the reflectors 16a, 17a and the red light and blue light dichroic mirrors 14a, 15a closer to the projection lens 13 to project an image on a screen 7 through the lens 13.
Since liquid crystals are exposed to very bright light in the liquid crystal projector 1, the temperature of the liquid crystal display units 8, 8a and 8b rises to a considerably high level.
Conventionally, therefore, the case 11 is provided with a fan (not shown) therein for cooling the units 8, 8a, 8b with air to prevent the rise of temperature.
However, because air is small in specific heat and further because the amount of heat transmission along the surface of glass is small, an attempt to use light of higher brightness gives rise to a need for the air cooling system to produce an increased amount of air current, consequently permitting the fan to give off a noise.
Unexamined Japanese Patent Publication HEI 1-159684 proposes an arrangement for forcibly circulating a liquid refrigerant to cool a liquid crystal unit. The arrangement, however, requires piping or circulation system for the refrigerant, is therefore complex in structure and has the problem of making the projector large-sized.